(1) Field of the Invention
The present invention relates to a coordinates input device using a liquid crystal sheet, more particularly, to a coordinates input device using a liquid crystal sheet in which, when a surface of the liquid crystal sheet is traced with a coordinates indicator or the like, the corresponding characters or figures appear as a liquid crystal display, and the coordinates of a handwriting drawn on the liquid crystal sheet are detected.
(2) Description of the Prior Art
Conventionally, there have been proposed various coordinates reading devices (also called a tablet) for use in inputting the coordinates of drawings or figures. Namely, when pointing devices such as a stylus pen and the like move on a surface of a tablet, its position is converted into coordinates position on a display screen (for example, a video monitor screen). As for coordinates reading devices, there are, for example, an electromagnetic induction type, a pressure sensitive resistant type, a pressure sensitive contacting type, an electrostatic capacitance coupling type and a magnetic coupling type.
As for tablets capable of displaying handwritings, tablets with active liquid display have been often seen recently. Here, the tablet with active liquid display is for displaying characters, figures and the like in the form of liquid crystal display by optically changing displayed dots corresponding to the detected input coordinates.
With the conventional former tablet described above, however, the pointing devices such as the stylus pen and the like are made to move on the surface of the tablet to input figures, characters or the like, so that inputted figures, characters or the like are displayed on the monitor screen, but the handwritings are not kept on the tablet. Thus, inconveniently, characters, figures or the like must be inputted by watching the monitor screen and moving the pointing device while replying on one's sense.
Moreover, when it is desired to add additional writings or decorations to characters, figures or the like which have been already inputted, the operator has to confirm the starting position of the drawing by reviewing the monitor screen since the tablet does not keep the handwritings of initially inputted characters, figures or the like. Naturally, the same problem exists for erasing a part of the image. Such writing and erasing operations have been considered too difficult.
The conventional latter tablet with active liquid crystal display, as compared with an externally charged liquid crystal sheet for liquid crystal displaying characters, figures or the like by externally applying an electrical charge, has the following problems.
a) The tablet with active liquid crystal display requires many operational processes due to application of feedback, and a responding speed to the coordinates input is slow when the same operational processing ability is provided. PA1 b) The tablet with active liquid crystal display requires an active element to drive the liquid crystal, which makes the structure of the liquid crystal display device itself complicated. PA1 c) The tablet with active liquid crystal display tends to be made thicker, and lacks flexibility. PA1 d) The tablet with active liquid crystal display employs a dot-display system, which lacks smoothness of characters. PA1 e) The tablet with active liquid crystal display is difficult to exchange the liquid crystal section. PA1 f) The tablet with active liquid crystal display does not keep displays when the power source is turned OFF. PA1 g) The tablet with active liquid crystal display is difficult to make its display section a wider screen.